Communicating without shared reference frames

Abstract

We generalize a quantum communication protocol introduced by Bartlett et al. [New. J. Phys. 11, 063013 (2009)] in which two parties communicating do not share a classical reference frame, to the case where changes of their reference frames form a one-dimensional noncompact Lie group. Alice sends to Bob the state $ρ_R \otimes ρ_S$, where $ρ_S$ is the state of the system Alice wishes to communicate and $ρ_R$ is the state of an ancillary system serving as a token of her reference frame. Because Bob is ignorant of the relationship between his reference frame and Alice's, he will describe the state $ρ_R \otimes ρ_S$ as an average over all possible reference frames. Bob measures the reference token and applies a correction to the system Alice wished to communicate conditioned on the outcome of the measurement. The recovered state $ρ_S'$ is decohered with respect to $ρ_S$, the amount of decoherence depending on the properties of the reference token $ρ_R$. We present an example of this protocol when Alice and Bob do not share a reference frame associated with the one-dimensional translation group and use the fidelity between $ρ_S$ and $ρ_S'$ to quantify the success of the recovery operation.